# Homework Help: Calc Conductivity of an intrinsic semiconductor

1. Aug 21, 2010

### nanostar

Calculate the conductivity of an intrinsic semiconductor at room temperature and from the following data:

(n)Carrier density(where electron=holes)=2.9*10^19 carrier/m^3
Electron mobility = 0.45 m^2/V s
Hole Mobility = 0.23 m^2/V s
(q)Charge per electron/hole = 1.6*10^-19 coulomb/carrier

I know that conductivity = nqu

but how do I include the e and h mobility too?

2. Aug 21, 2010

### ehild

What is the conductivity if there are two kinds of charge carriers?

ehild

3. Aug 21, 2010

### nanostar

????

4. Aug 21, 2010

### ehild

From Wikipedia:

When there is more than one species (e.g., a plasma with electrons and ions, or a semiconductor with electrons and holes), the total conductivity is
σ = ∑ niμi | qi |
i

where the ith species has number density ni, charge qi, and mobility μi.

ehild

5. Aug 27, 2010

### GabbleRatchet

σ = neqeμe+nhqhμh

Where the subscripts are electron and hole respectively.

You have to account for the fact that the carriers are of opposite charge and travel in opposite directions (I think). If in doubt, you can always ask on Thursday...